This invention relates to methods and apparatus for cutting vegetation and the like, and more particularly relates to improved lawn mowing methods and apparatus.
It is now common practice to provide a greensward in conjunction with most residential and other structures intended for human use and occupancy, not only to enhance the overall esthetic appear of such structures, but also to provide an area associated therewith for purposes of recreation and relaxation. It is also common practice to maintain such greensward in a mowed condition to further enhance its usefulness in this regard, and thus various forms of mowing devices have been devised and employed to more effectively mow such areas.
Many different forms of apparatus have been devised and made available for mowing a greensward and the like, although most of these devices may be characterized as either a "reel-type" mower or a "rotary-type" mower. Both of these types of mowers are sufficiently well known so as not to require explanation, except to note that they both employ one or more moving steel blades to sever the grass to a substantially uniform height. It is also well known that the rotary-type mower is inherently more dangerous to persons and property. It is also the most popular type of mower because it is easier to use and also because it is better suited to areas where the grass is either tall or thick or both.
What has not been generally appreciated is the likelihood of serious injury attaching to the use of a conventional rotary-type lawnmower employing a rigid steel blade. However, the National Electronic Injury Surveillance System has estimated that, during 1973 alone, there were 53,350 mower-related accidents serious enough to require hospital treatment.
The manufacturers of rotary-type lawnmowers have not been indifferent to this problem, of course, and have made strenuous efforts to provide against such injuries. For example, all mowers are provided with covers or "shrouds," not only to enclose the blade but also to route stones and other debris struck by the blade along a restricted predetermined route. In addition, these mowers are mounted on widely spaced wheels of relatively small diameter so as to improve their stability. There is a practical limit to such measures, however, and thus a conventional rotary-type mower will apparently always constitute a source of serious injury.
Because of this problem, there have been various attempts to change the basic design of this type of mower or to adopt other radical changes. For example, there is shown in U.S. Pat. No. 2,557,598 a lawn mower which is generally conventional in its overall appearance but wherein the rigid steel blade has been replaced by a disc having a plurality of metal wires extending radially from its perimeter. These wires have substantially less mass than a conventional mower blade, of course, and they are more flexible, and thus more yieldable, under impact. Nevertheless, a revolving steel rod or wire is only slightly less dangerous than a rigid blade, and will project debris with only slightly less force. Also, such a mower is significantly less effective for grass-mowing purposes.
In U.S. Pat. No. 3,091,915, there is disclosed another lawn mower wherein the lower portion of the shroud is provided with a grille-like plate with apertures for admitting the upward thrust ends of the grass and with honed edges at the apertures in the grille plate. The blade is replaced with a brush-like assembly which revolves over the plate to "wipe away" the grass ends sought to be cut, by drawing them over the honed edges in the grille. The bristles of the brush assembly are sufficiently stiff so as to cause the grass to be severed, but they are also sufficiently flexible so as not to project debris in a dangerous manner or to injure any portion of the body which may be inadvertently inserted through the grille member. There can be no dispute that such an arrangement, wherein the cutting member (the grille) is held stationary, is inherently safer than is a revolving steel cutting blade. Cutting effectiveness is basically a function of impact, however (except in a scissor-like arrangement), and thus a mower of this design is only limitedly effective when used in areas having high or dense vegetation.
In U.S. Pat. No. 3,208,209, the conventional rigid blade is replaced with a disc-like member having a plurality of relatively short and resilient wires extending from its periphery. When the disc-like member is revolved, the wires are sufficiently stiff so as to sever vegetation, but are sufficiently flexible so as to yield to any so-called "foreign" object. As will hereinafter be made apparent, however, such an arrangement will not achieve effective mowing without the addition of other features.
In U.S. Pat. No. 3,302,377, there is disclosed a novel cutting member intended to replace the rigid blade in a conventional rotary-type mower and which is formed of composite molded rubber reinforced longitudinally by less elastic fibers. It is claimed that such a blade will either yield to foreign objects such as a shoe sole and the like, or will discharge rocks and other debris at safer velocities. It is also admitted, however, that such a blade is subject to wear during use and that it has a limited useful lifetime.
In U.S. Pat. No. 3,320,732, there is disclosed apparatus which is also intended to replace the conventional rigid metal blade in a rotary lawnmower and which includes a revolvable disc having a pair of non-metallic blades mounted at opposite points on its perimeter. Although the blades are preferably formed of a plastic such as polyurethane, they are intended to be wide enough so as to be substantially rigid, whereby effective cutting is achieved. On the other hand, pivotally attaching the blades to the disc permits them to yield upon encountering a foreign object.
Other examples of devices and apparatus intended to replace the rigid steel blade in a conventional rotary lawnmower may be found in U.S. Pat. Nos. 3,340,682, 3,389,541, 3,444,675, 3,474,608 and 3,664,102. However, none of these or the other innovations cited herein have been a solution to the problem, and thus the rotary lawnmower with a rigid steel blade has continued to be the most widely used device for these purposes.
Recently, a completely new type of vegetation cutting device has been developed and marketed under the trademark "Weed Eater," which device is depicted generally in U.S. Pat. Nos. 3,708,967, 3,826,068 and 3,859,776, and which employs one or more flexible non-metallic cords which are revolved to function as cutting elements. This type of device has enjoyed spectacular commercial success as an edger/trimmer, since it provides a number of advantages which cannot be found in conventional cutters. For example, these cutters are capable of reaching into areas not accessible to rigid steel blades and the like, and thus the Weed Eater trimmer can remove weeds and other vegetation located in close proximity to walls, fences, trees and even within crevices in such walls and the like, without damage to such walls and trees. Second, and more important for present purposes, the Weed Eater trimmer is substantially completely safe to operate since the revolving cords will cause injury under only the most unusual circumstances.
Because of these advantages, as well as others, it has been proposed to construct a lawn mower incorporating this principle to thereby eliminate the hazards which are inherently present with conventional mowers. More particularly, it has been proposed to replace the rigid steel blade in such mowers with a head assembly having one or more such flexible cords and to revolve such assembly and cords to sever the grass on a greensward. This proposal has proved to be deceptively oversimple, however, and is based on a misconception that the Weed Eater edger, as presently built and marketed, is the functional equivalent of a conventional lawn mower. Accordingly, all such attempts to construct an operable lawn mower employing such a cutting element have hitherto been failures for the reasons hereinafter set forth.
It is common practice to broadly characterize all powered grass and weed cutting devices as "lawn mowers," excepting those machines intended to be used by commercial agriculturalists and the like. There is a basic functional distinction between a lawn mower per se, however, and a device which is more accurately denoted as an "edger/trimmer," and this distinction must be clearly understood to appreciate the reason why it has not been possible to merely replace a steel blade with a Weed Eater trimmer head assembly.
The basic principle of any lawn mower per se is that the cutting element or elements are manipulated strictly within a cutting plane which is fixedly located relative to the surface of the area being mowed. The reason for this is that the very concept of "mowing" contemplates the leveling of the grass to produce a carpet-like effect, and thus the blade must be rotated in a plane which is fixedly positioned relative to the surface of the earth. Otherwise, the greensward would have a ragged, uneven appearance after being cut, and this is not the effect or result sought to be achieved.
When a rigid steel blade is revolved in this plane, it yields to the grass only to the extent that it may tend to slow, but it does not become warped or distorted so as to be deflected from its intended cutting plane. If a flexible non-metallic string is revolved to cut vegetation, however, it yields to the grass in various ways. In particular, it not only yields laterally in that it assumes a curvilinear configuration, but it also tends to be deflected upward by the grass it is cutting. Accordingly, if the cords of a Weed Eater are brought into contact with resistant vegetation, these cords tend to move in a cutting "plane" which actually has a warped configuration.
This warping effect is an advantage of the Weed Eater edger/trimmer, since it is this which enables its user to manipulate its cords to cut away the most inaccessible vegetation. When a mower is constructed in the manner of the Weed Eater trimmer, however, this warping effect tends to produce swaths having convex configurations, and this is extremely undesirable from an esthetic standpoint.
An edger/trimmer, and especially the Weed Eater trimmer, is not intended as a leveler, per se, but as hereinbefore stated, is intended to reach vegetation growing in otherwise inaccessible locations. Thus, an edger/trimmer must provide a cutting plane which can be manipulated into a variety of angles with respect to the surface of the earth and, in the case of the Weed Eater edger, must be capable of non-alignment of its cutting elements relative to its normal cutting plane. The Weed Eater trimmer as presently designed and marketed is carried by the operator so as to facilitate such manipulation. Even an edger/trimmer using a revolving steel blade is supported on no more than two spaced-apart wheels in order that its cutting plane may be tilted as needed.
Another functional difference between a rotary-type mower and an edger/trimmer is the diameter of their cutting planes. Cutting actually is accomplished at the tip of the cutting element, whether the element is a flexible cord or a rigid steel blade, and since cutting is a function of tip velocity, it will be apparent that the diameter of the cutting plane must be such as to provide for effective cutting. In the case of a lawn mower, however, the prime consideration in selecting the proper diameter of the cutting plane is the width of the swath sought to be cut.